Selective solvent for silver.



UNITED STATES PATENT OFFICE.

SELECTIVE SOLVENT FOR SILVER.

, Specification of Letters Patent.

ratented July 31, 1906.

Application filed July 18, 1905. Serial No. 270.300-

To 00% whom it may concern:

Be it known that I, FRANCIS J. HoBsoN, a citizen of the United States, now residing at Guanajuato, in the Republic of Mexico, have invented certain new and useful Improvements in Selective Solvents for Silver, of which the 'ioliowizig is a s cei'freation.

My present invention consists of a selective solvent for silver in ores the action of which has some points of aflinity with and some of difference from that of cyanid solutions in dissolving silver or gold. It is particularly useful in those ores in which the silver is present in combination with sulfur, and as sulfur is present in almost all silver ores the selective aflinity which forms the great utility of my invention is nearly always brought into play.

The particular solvent which I have devised and the selective action of which I have experimentally demonstrated many times is a mercurous potassic cyanid the formula of which is KI IgCy and which forms with silver when present with sulfur a double salt,

the cyanid of silver and potassium, freely soluble in water, and the sulfid of mercury, substantially insoluble in water and in ordinary metallurgical processes forming a part of the residue. The reaction to which I have referred may be expressed verbally as follows: silver sulfid-l-mercurous potassic cyanid cyanid of silver and potassium sulfid pf mercury, or, in chemical symbols, as folows:

verb ally as follows: silver cyanid of potassium oxygen water cyanid of potassium and silver potassium hydrate or caustlc potash, and in chemical symbols is represented thus 2Ag+ iKCy+O+ H2O I QKA gCm-tZKOH.

Free oxygen in solution is necessary to dissolve silver and form the double salt of potassium and silver with cyanogen. The same equation applies to the solution of gold, gold replacing silver in it.

I may produce the mercurous potassic cyanid in any-desired way, since the particular method of its production does not seem to affect the results. I may, for example, add

mercurous chlorid (Hg Cl to a solution of potassium cyanid, (KCy) Another method which I may use is to add mercuric chlorid (corrosive sublimate HgCl to the ordinary mill cyanid solutions containing ferrocyanid of potassium. The reaction here may be expressed verbally as follows: ferrocyanid of potassium mercuric chlorid ferrocyanid of mercury chlorid of potassium, or, expressed in chemical symbols,

followed by the reaction which may be expressed verbally, thus: ferrocyanid of mercury+ cyanid of potassium=ferrocyanid of mercury and potassium+mercurous potassic cyanid, or, expressed in chemical symbols,

The most suitable strength of the solution of the salt is of course to some extent dependent upon the silver content of the ore and the form in which the metal is present; but I have obtained good results with solutions from .05 to .50 per cent.

The metal may be separated from the solution in any of the approved methods used in the cyanid processes commonly employed, as by precipitation by zinc-dust or shavings, electrolysis, &c.

So far as I am aware, I am the first to use the described salt as a selective solvent for silver, whether in the precise manner suggested in the foregoing description or in other ways, and that feature I wish to protect by my claims.

In order to obtain the best results, the solution should be kept alkaline, and this may be effected by the addition of any suitable alkali, such as caustic potash or soda, although in most cases lime will be found to be not only the cheapest but the best alkali. Such changes as are necessary to adapt the solvent and the process of using it to the ordinary difiiculties arising in the treatment of varying ores I regard as within the skill of all combination with sulfur, a solution of potascompetent metallurgical chemists, who will sium cyanid to which has been added merbe able to apply the new agent under varying 1 curous chlorid. conditions from the directions contained in i 5. As a selective solvent for silver when in 20 5 the foregoing specification. combination with sulfur, an alkaline solu- Having thus described my invention, what tion of potassium cyanid to which has been I claim, and wish to protect by Letters Pat- 5 added mercurous chlorid. ent of the United States, is- 6. As a solvent for silver in the presence of 1. As a solvent of silver, a mercurous salt sulfur, a solution of mercurous potassic cy- 25 10 of cyanogen and an alkaline metal. anid, having the formula KHgCy and of ap- 2. As a solvent of sillveil an alkaline spluproximately .05 to .50 per cent. in strength. tion of a inercurous sa t o c anogen an an T alkaline metal I y ll FRANCIS J. HOBSOh.

3. As a solvent for silver in ores, a solution Witnesses: 15 of inercurous potassic cyanid. T. J. JOHNSTON,

4. As a selective solvent for silver when in MARY AGNES NELSON.

It is hereby certified that in Letters Patent No. 827,368, issued July 31, 1906, upon the application of Francis J. Hobson, of Guanajuato, Mexico, for an improvement in Selective Solvents for Silver, errors appear in the printed specification requiring correction, as follows: In line 71, page 1, the symbol HgOl, should read 2HgOZ,; same page, line 8, after the word ores, line 20, after the word devised, line 21, after the Word times, line 22, after the word cyanid, and line 40, after the word silver, commas should be inserted; line 23, after the formula, a semicolon should be inserted, and line 41, after the word manner, the comma should be stricken out and D a semicolon inserted instead; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 18th day of September, A. D., 1906.

E. B. MOORE,

Acting Commissioner of Patents.

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